Wolff, Christian, Freiherr (Baronbaron) vonWolff also spelled Wolf ( born Jan. January 24, 1679 , Breslau, Silesia [now Wrocław, Pol.Poland]—died April 9, 1754 , Halle, Prussia [now in Germany] ) philosopher, mathematician, and scientist who worked in many subjects but who is best known as the German spokesman of the Enlightenment, the 18th-century philosophical movement characterized by Rationalism.

Wolff was educated at the universities of Breslau, Jena, and Leipzig and was a pupil of the philosopher and mathematician Gottfried Wilhelm Leibniz. On the recommendation of Leibniz he was appointed professor of mathematics at the University of Halle in 1707, but he was banished in 1723 as a result of theological disputes with Pietists, who were followers of the German movement for an increase of piety in Lutheran churches. He became professor of mathematics and philosophy at the University of Marburg, Hesse (1723–40), and, as science adviser to Peter the Great (1716–25), he helped found the St. Petersburg Academy of Sciences in Russia. After returning to the University of Halle, at the request of the king of Prussia, Frederick II the Great, he became chancellor (1741–54).

Wolff wrote numerous works in philosophy, theology, psychology, botany, and physics. His series of essays all beginning under the title Vernünftige Gedanken (“Rational Ideas”) covered many subjects and expounded Leibniz’s theories in popular form. Wolff emphasized that every occurrence must have an adequate reason for happening or there arises the impossible alternative that something might come out of nothing. He applied the rational thought of the Anglo-French Enlightenment and of Leibniz and René Descartes in the development of his own philosophical system, the Wolffian philosophy. Rationalism and mathematical methodology formed the essence of this system, which was an important force in the development of German philosophical thought.